Reproductive Outcomes for Dairy Heifers Treated with Combinations of Prostaglandin F₂, Norgestomet, and Gonadotropin-Releasing Hormone

¹ Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201
² Department of Animal and Range Science, New Mexico State University, Las Cruces 88003-0003

We conducted three experiments to test various protocols for synchronizing estrus, ovulation, or both before insemination of heifers. In experiment 1, 23 controls received two PGF₂ injections; 23 heifers were treated like the controls plus a norgestomet implant for 8 d, with the second PGF₂ injection 24 h before implant removal; and 23 heifers were treated like the previous group plus 100 µg GnRH 54 h after the second PGF₂ injection. Although norgestomet and GnRH altered some estrual characteristics, conception rates in experiment 1 (n = 69) and experiment 2 (278 heifers receiving the same treatments as those in experiment 1) generally were not different among treatments. Reproductive outcomes were not improved by adding norgestomet and GnRH to a standard PGF₂ protocol. In experiment 3, control heifers received PGF₂ and were inseminated after detected estrus or at 72 to 80 h after a second injection of PGF₂ given 14 d after the first injection. Select Synch heifers, treated with GnRH either 6 or 7 d before PGF₂, were inseminated after detected estrus, whereas Ovsynch heifers were treated like Select Synch heifers but also received a second GnRH injection approximately 36 h after PGF₂ and were inseminated 18 h later. Estrus detection and pregnancy rates after Ovsynch were less than those of controls, whereas conception and pregnancy rates did not differ between control and Select Synch heifers. Therefore, the Select Synch protocol was equivalent to a standard PGF₂ protocol, whereas Ovsynch was inferior to both of those protocols.

Key Words: estrus synchronization • heifers • hormones • timed artificial insemination

Submitted on November 3, 1999
Accepted on March 14, 2000

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